Asked by: Xu Beortegui
home and garden indoor environmental quality

Which wire is power on thermostat?

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The R (red) wire is really the power source. The C wire closes the circuit and allows continuous flow of 24V energy to power the thermostat.


Besides, where does thermostat get power?

Most room thermostats on heating and cooling systems receive their 24V DC electrical power from a low voltage transformer that itself is usually found at the boiler or furnace (blue arrow in our photo at left).

Beside above, how are thermostats wired? Power from the air-conditioning transformer comes into the terminal labeled RC. The ball controlled by the mode switch jumps the current onto a trace that leads to the terminal in the lower-right corner of the circuit board. This terminal connects to the top layer of the thermostat through a screw.

Beside above, what is the blue wire on a thermostat?

The blue wire, or C-wire, is known as the common wire. It's there to provide power to the thermostat. Older thermostats usually don't have a C-wire because they either don't need power or, if they do, they get it from a battery. Modern thermostats are a different story.

Is the C wire a ground?

The C wire is the common wire ground wire. You already have 24v ac going to the red wire. If you have an extra wire connect it to the C at the thermostat and ground it at the transformer box in the AC unit.

Related Question Answers

Nani Muromtsov

Professional

Why is there no power to my thermostat?

The power is out or a circuit breaker has tripped
The power loss could also be the result of a tripped circuit breaker that powers the air conditioner or heater. Many thermostats run on low voltage sent from the transformer on the HVAC system; if the transformer loses power, so will the thermostat.

Meagan Uliarte

Professional

How do I know if my thermostat has power?

How to Check If Power Is Getting to My Thermostat?
  1. Check the circuit breaker. Go to your breaker box and look for the breaker that powers the furnace or air conditioner.
  2. Check the power switch. There is power switch on the side of the HVAC unit.
  3. Change the batteries in the thermostat.
  4. Test the power wire to the thermostat.

Criselda Galtieri

Professional

Does a thermostat need power?

Most digital or WiFi thermostats require power to operate. Power: Provides power from the transformer on the furnace or boiler. Power for Cooling: Provides power for the cooling cycle. If the heating and cooling systems share a transformer then a jumper may be connected between the Rh and Rc terminals.

Yoshie Tcharnolusky

Explainer

Where is the fuse for the thermostat?

Simply locate your breaker panel or fuse box (usually either outside your home or located in a closet somewhere inside) and look for the fuse or circuit that your furnace is on.

Doreatha Avila

Explainer

How many wires does a thermostat need?

In the most basic system, this functionality is provided by use of a fan center relay, and the low voltage wiring to the thermostat now will require a minimum of three wires (for heat only units) and four wires (for heat / cool / fan) for control.

Candid Chale

Pundit

Where is the fuse in AC unit?

A fuse is a metal filament or wire, usually in some type of casing. It's located in the disconnect box, connected to your AC. It is there to protect your machine, to avoid more serious problems.

Nele Knaack

Pundit

Do all thermostats have batteries?

The bottom line: Yes, thermostats need batteries unless, of course, the thermostat in your home is only powered by the main grid. But if your home's thermostat has a battery compartment, you should place batteries in it.

Jordi Saifitdinov

Pundit

What color is the C wire?

Here are common uses for wire colors: Blue or Black – C – Common wire, may be unused by your existing thermostat. Enables continuous power flow from the Red wire. Red – R – 24VAC power from the furnace's transformer.

Salobral Monclova

Pundit

What does a blue wire mean?

Blue and yellow
Yellow and blue electrical wires are also used to carry power but are not for wiring the outlets for common plug-in electrical devices. These colors are used for the live wire pulled through conduit. You'll use blue mainly as a traveler for a three-way or four-way switch.

Zona Kinder

Pundit

What color is the common wire?

The "common" is the "neutral" or "ground" wire, depending on the type of circuit. In normal US residential wiring, you'll have a black "hot" wire, a white "neutral" or "common" wire, and a green or bare "ground" wire.

Melibea Schuren

Teacher

What color wire goes where on a thermostat?

Most thermostats have a Red wire that is the power wire that usually connects to R & RC terminals of the thermostat, a Green wire that energizes the Fan relay, connected to the “G” terminal on the thermostat, a Yellow wire that energizes the outdoor unit's contactor, (if you have air conditioning) and a white wire that

Fatema Espinosa

Teacher

What happens if you wire a thermostat wrong?

Electric shock. Damaging the thermostat unit, the electrical system or even the AC/furnace unit itself. Dual-fuel systems, a poorly located thermostat, whole-home humidifiers, or incorrect wiring can make the installation of a thermostat a longer, more frustrating, and more complicated process.

Ossama Sabarich

Teacher

How do I know if my thermostat has AC wire?

It is easy to see if you already have a c-wire connected to your system. Simply remove your current thermostat face from its baseplate and look for the terminal labeled with the letter “c.” If this terminal has a wire attached to it, you have an active “c-wire.”

Hassna Lysansky,

Reviewer

How do I install a WIFI thermostat without C wire?

To add a C-wire to your furnace, follow these steps:
  1. Turn off the breaker for the furnace.
  2. Remove the access panel and locate the wires that connect to the thermostat.
  3. Disconnect the thermostat wire from the G terminal.
  4. Note: If you have both central heat and air, then you'll need to make a jumper using an 18 AWG wire.

Jader O'Neal

Reviewer

Why is my thermostat draining batteries?

The simplest answer is also the most likely: The thermostat is old or just faulty. The temperature settings you program into a digital wall thermostat don't impact battery usage (e.g., turning down the air conditioning in the summer won't save the battery life of your thermostat; you'll just save on your energy bills).

Mateusz Saurwein

Reviewer

What is common wire?

A common wire is a more general term and simply refers to the 0 Volt wire of a circuit, either electrical or electronic.

Arancha Borobio

Supporter

How do old thermostats work?

Once you've set the temperature, the thermostat is supposed to switch the heating on and off, as necessary, to keep the room more or less that warm. In practice, a thermostat like this doesn't switch on and off at a single temperature but cycles between a small range of temperatures either side of the value you set.

Andy Bartling

Supporter

How do you jump a thermostat?

Lift the ends of the jumper wire and move one end to the "Y" terminal and the opposite end of the jumper wire to the "G" terminal. The furnace fan should start operating. If the furnace and the fan start using the jumper wire, the thermostat requires replacement. If they do not, there is a problem within the furnace.

Zulima Sanchez Izquierdo

Supporter

What is R and RC on thermostat?

RC is no different and simply means red cooling. The wire is generally red, although there is no color standardization -- but more importantly, the "R" really means that the wire and terminal are hot; it's a live electrical wire. The RC wire connects to the RC terminal, which controls the cooling system.

Co-Authored By:

EveryThingWhat Staff Editor

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4th May, 2020

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